Near field communication (NFC) involves short range communication using magnetic induction between two loop antennas. Magnetic induction is a relationship between an electromotive force and a time varying magnetic field. By varying the magnetic field of one loop antenna, an electric current can be induced in the other antenna. In this sense, the combination of the two loop antennas can be conceptualized as an air-core transformer where the magnetic induction between the two windings of the transformer allows two devices to be communicatively coupled without being in physical contact.
One advantage of NFC is that only one of the devices involved in an NFC session needs to be a powered device, and the other can be a passive card, tag, or sticker. As a powered NFC device provides a signal to a passive device, the current that is induced in the passive device also provides power to that device. As a result, NFC has wide ranging applications in advertising (e.g., a consumer held reader communicating with a passive poster or sticker), ticketing (e.g., a ticket kiosk reader communicating with a passive ticket), and payments (e.g., a point of sale (POS) reader communicating with a passive smart card). Adoption of NFC by certain payment processing consortia has increased its potential for widespread adoption and has contributed to the inclusion of NFC technology in many smart phones and other devices.
The potential inclusion of NFC technology in a smart phone, tablet, POS, or other device has created an interesting design challenge. These devices often include other functionality such as radio antennas for longer distance wireless communication, touch displays, gyroscopes, and accelerometers that are packed into sleek and compact form factors. This additional functionality can interfere with the NFC communication pathway. For example, the touch screen, with its display and touch stack, serves as a barrier for NFC communication. Prior solutions have included placing the NFC antenna outside the lateral scope of the display in order to communicate around the display. A specific example of these kinds of approaches can be described with reference to device 100 in FIG. 1.
Device 100 includes a display 101 in a device frame 102. Device 100 provides an example of placing the NFC antenna outside the lateral scope of the display because frame 102 includes an embedded inductive near field communication antenna 103 with a coil pattern that extends around the entire lateral extent of display 101. Note that the coils of antenna 103 are shown in the drawing for illustrative purposes, but would be covered by a thin layer of protective frame material in actual use. As a result of this configuration, device 100 is able to create an electromagnetic field in direction 104 rising from frame 102 in order for device 100 to communicate with another NFC device without display 101 interfering with that communication pathway.